This invention relates to a fuel injection control device for an internal combustion engine and more particularly to an improved electrically operated fuel injection system for such engines.
The use of electrically operated fuel injectors for internal combustion engines is being widely accepted. The use of fuel injection and particularly that having electrical control permits more accurate control of the fuel air ratio under all running conditions and thus can offer both improvements in fuel economy and exhaust emission control.
Conventionally electrically operated fuel injectors employ an injection valve that is energized by an electrical solenoid so as to control the initiation of fuel injection and the timing of fuel injection by switching the solenoid. The solenoid is normally operated by a driver circuit which is controlled by a control circuit that provides a control signal to the driver circuit so as to energize and deenergize the solenoid of the fuel injector. In most applications, the control circuit and the driver circuit are supplied with electrical power from a power source such as a battery.
It is desirable to insure control of the voltage and power supplied to the circuits and for these purposes there are normally incorporated an electrical source circuit that provide a controlled voltage to the arrangements, However, with most conventional arrangements the electrical source circuit supplies the controlled voltage to both the control circuit and the driver circuit. This type of prior art arrangement is shown schematically in FIG. 1 and will now be described by reference to that Figure.
This may be seen in FIG. 1, there is provided a fuel injection control circuit for actuating a plurality of fuel injectors and specifically the solenoid actuating coils 11a, 11b, etc., therefore. The system is supplied from electrical power from a battery, indicated schematically at 12. The battery has one of its terminals connected to a control circuit, indicated schematically 13 which includes a constant voltage supply circuit 14 that outputs a constant voltage power source to a CPU 15 which, in turn, outputs control signals to a driver circuit, indicated generally by the reference numeral 16. The CPU also receives data from engine and/or ambient sensors to determine the appropriate timing and duration of fuel injection. These control signals are transmitted over conductors 16a, 16b, 16c, 17a, 17b, etc.
The driver circuit, in turn, has a control circuit that is powered by the constant voltage supply circuit 14 of the control circuit 13 as via a conductor 18 and switches a plurality of switching circuits 19a, 19b, etc., in response the control output signals from the CPU 15 with the control circuit indicated generally by the reference numeral 21. The switching circuit 19a alternately completes the circuit through the solenoids 11a, 11b, etc., of the fuel injectors for causing their operation. The injectors 11a, 11b, etc., are all supplied with voltage with the battery 12 through a line 22 which is common for all injectors as is the return line to the battery 22 which return line is indicated by the reference numeral 23 and also provides the return from the controller 21 and CPU 15.
Although this type of prior art circuit has the advantages of simplicity, there are number of difficulties with it that adversely affect the performance. First, since the control circuit 13 and the driver circuit 16 are powered by the same constant voltage supply 14, the noise of the driver circuit 16 is transferred to the control circuit 13 and the control circuit 13 may, therefore, misfunction. Also, since the electric voltage from the supply circuit 14 is supplied to the driver circuit 16 the driver circuit 16 must be designed so as to accurately actuate each injector and this can provide problems in circuit design. Also since the control lines 22 and 23 for the injectors 11a, 11b are common, this also tends to cause noise between the various injectors with attendant possible malfunctioning.
It is, therefore, a principle object of this invention to provide an improved, simplified and yet highly effective control device for electrically operated fuel injectors for an internal combustion engine.
It is a further object of this invention to provide an electrical control circuit for a fuel injection system for an engine that will be more accurate and minimize the likelihood of misinjection due to noise in the electrical circuitry.